Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across San Francisco
Adding square footage in San Francisco means working with wood-frame Victorians, steep lots, fog-dampened lumber, and one of the strictest permit departments in California. A full home addition here typically lands between $53,100 and $153,400, while a detached ADU runs $106,200 to $259,600. We’re Barrett & Sons Construction, and we’ve been pulling permits and pulling nails in San Francisco long enough to know which homes hide dry rot behind the siding and which inspectors want photos of the foundation bolts. Call (877) 610-1318 and Tom will answer, or his sons will. That’s how it works here.
Why Barrett & Sons Construction Is San Francisco’s Preferred Home Additions & ADU Company
San Francisco homeowners call us after another contractor has already burned them. That pattern is so common it could be a neighborhood. We get the call from a Noe Valley homeowner whose “permit-exempt” addition turned out to need an abatement, or a Visitacion Valley family whose previous bid didn’t include foundation pins. Tom Barrett publishes his name, his address, and his license number. Look it up before you sign anything. The permit inspector works for you, not for me, and that’s exactly why we like having him on the job.
Our crew members are Tom’s sons and their teams, background-checked and uniformed on every visit. You’ll see the same faces on day three that you saw on day one, and those faces live in the Bay Area. A live person answers the phone 24/7, not a voicemail box in another state. Every scope, every allowance, every price change arrives as a written change order before work happens. No surprise invoices. The allowance that isn’t on paper is a surprise waiting for a date.
We’ve done additions and ADUs in every corner of San Francisco, from the flatlands of the Mission District to the fog-driven moisture problems on the western slope. That local knowledge matters when your 1912 Edwardian needs a seismic upgrade before the addition can pass inspection, or when your hillside lot requires a soils report that nobody mentioned in the first bid. We mention it in writing, on day one. And we back every completed San Francisco job with the written 90-Day Done Right Promise. If it’s not done right, Tom comes back and makes it right. One call.
Our Home Additions & ADU Services in San Francisco
ADU Design & Permitting
Getting an ADU approved in San Francisco means navigating the Department of Building Inspection, not just submitting a drawing. The city’s layered permit process routinely adds months to projects that would clear in weeks in Oakland or San Jose. We handle the design, the structural calcs, the DBI submittals, and the inspections that follow. If your property sits in ZIP 94122 or 94123, your lot coverage and rear-yard setback rules are different from a Mission District infill lot, and we plan for that from the first site visit.
Garage Conversion ADU
Many San Francisco garages are tuck-under spaces in pre-1978 wood-frame buildings, which means the city’s Soft-Story Retrofit Ordinance may already require structural work at the ground floor. Converting that garage into a legal ADU often triggers the very retrofit your building needs anyway. We coordinate the two scopes so you’re not paying twice for the same engineering. A garage conversion in San Francisco usually runs $35,400 to $94,400, depending on whether the foundation needs shear-wall reinforcement and whether we’re correcting drainage that’s been seeping through the slab for decades.
New Detached ADU
A new detached ADU in a San Francisco backyard is a different animal from an interior conversion. You’re dealing with setback relief, often a new sewer lateral, and a foundation engineered for whatever’s under your lot. On the eastern side of town, that could be bay mud and 19th-century landfill, which means deep piers or grade beams. On the bedrock of the western hills, a standard footing may be fine. We tell you which one applies to your address, in writing, before you commit. Detached ADUs in San Francisco typically cost $106,200 to $259,600.
Junior ADU & Interior Conversion
A junior ADU, usually 500 square feet or less carved from an existing floor plan, is the fastest legal path to rental income in San Francisco. The city’s ADU ordinance allows JADUs in neighborhoods where a full detached unit would never clear setback review. We convert attics, basements, and rear bed spaces into code-compliant units with their own entrance, kitchenette, and bathroom. Interior conversions often run at the lower end of San Francisco’s home addition range, and they’re frequently what makes a Victorian in Noe Valley or the Mission pencil out for a multigenerational family.
If your addition involves reconfiguring the existing footprint, our Home Additions & ADU team often works side by side with our Kitchen Remodeling in San Francisco crew, since a rear addition usually means a new kitchen wall. And when the plan calls for a second bathroom, our Bathroom Remodeling in San Francisco team handles the wet work under the same permit, same schedule, same written change orders.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in San Francisco
We install materials you can look up, not mystery brands off a van. On San Francisco ADU and addition jobs, that means Schluter waterproofing systems in bathrooms and wet rooms, Sterling and Grohe fixtures where the budget allows, and GAF roofing where an addition ties into an existing roof plane. The marine layer here means a bad waterproofing detail doesn’t show up in the first winter, it shows up in the third, after the mold has had time to work. We stock the right substrates and membranes for coastal moisture, and we warranty what we install.
Common Home Additions & ADU Problems We See in San Francisco Homes
- Chronic moisture and dry rot in framing. San Francisco’s year-round fog, especially in the Sunset and Richmond ZIPs, keeps exterior lumber damp for months at a time. We regularly open walls on 100-year-old row houses and find sill plates that crumble when you put a screwdriver to them. An addition that doesn’t address the rot is just a new room attached to a dying one.
- Foundations never engineered for seismic loads. The Victorian and Edwardian housing stock built between 1880 and 1915 often sits on raised post-and-pier foundations with no lateral resistance to speak of. Any significant renovation triggers a foundation assessment, and usually a shear-wall or anchor-bolt upgrade as a condition of permit approval. We plan for that cost in the first written estimate, not as a surprise change order.
- Lead paint abatement on pre-1978 properties. Nearly all of San Francisco’s original housing stock predates the 1978 lead paint ban. Cutting into walls for an addition means compliance with the EPA’s Renovation, Repair, and Painting rule, and the Department of Public Health tracks this. We run certified lead-safe work practices on every job site, and it’s already built into our pricing.
- Liquefaction risk on bay mud. In SoMa and along the northern waterfront, the Loma Prieta earthquake showed exactly what landfill does when it shakes. Foundation work there routinely requires deep piers or grade beams, and an engineer’s soils report is the first document we order. A bid that skips that step is a bid you should throw away.
Pricing for Home Additions & ADU in San Francisco, CA
You want numbers. Here they are. A standard room addition in San Francisco runs $53,100 to $153,400, depending on foundation work, seismic upgrades, and whether you’re matching Victorian trim or going clean and modern. A new detached ADU ranges $106,200 to $259,600. A garage conversion typically lands $35,400 to $94,400. A junior ADU or interior conversion usually falls in the $53,100 to $94,400 window, because you’re working within existing walls but still meeting DBI requirements for egress, ventilation, and fire separation. The four biggest cost drivers in San Francisco are foundation condition, permit timeline, hillside access, and whether the existing structure needs a seismic retrofit before the addition can pass inspection. We give you a written line-item quote, free, before you sign anything. Call (877) 610-1318 and ask for Tom. If he’s on a ladder, one of his sons will pick up.
We Also Serve Cities Near San Francisco
Our crews work throughout the city and into the surrounding neighborhoods, so if you’re in Mission District, Noe Valley, Chinatown, or Visitacion Valley, you’re still San Francisco to us. We know the permit counter at DBI, the parking situation on 24th Street, and which hillside streets need a traffic control plan. Same crew, same written change orders, same 90-Day Done Right Promise.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Home Additions & ADU in San Francisco
We can typically get a site visit scheduled within a few days of your call, and the real timeline after that is set by the Department of Building Inspection, not by us. A straightforward interior conversion with over-the-counter permits can start in a few weeks. A detached ADU needing Planning Commission review or a variance can take several months before we’re allowed to swing a hammer. Call (877) 610-1318 and we’ll tell you which track your project is on, in plain English.
Yes. We work in every ZIP from 94122 through 94125, plus the eastern neighborhoods from SoMa to Visitacion Valley. That includes the Mission District, Noe Valley, Chinatown, the Sunset, the Richmond, and everywhere in between. We know which streets need a parking permit for the crew truck and which inspectors want photos of the foundation bolts before they’ll sign off. Call (877) 610-1318 for a free estimate at your address.
A home addition in San Francisco costs $53,100 to $153,400, and the gap between that number and what you’d pay in Oakland or San Jose is driven almost entirely by permit timelines and seismic requirements. DBI review routinely adds months, and engineering costs for soft-story retrofits or liquefaction mitigation are simply not optional here. You’re paying for the privilege of building on some of the most expensive, most regulated land in the country. We price the work honestly, with every allowance in writing before the first nail moves. Call (877) 610-1318 for an exact quote.
Only if the scope changes in writing. That’s our rule, and it’s been our rule since Tom founded this company in 1998. If the foundation turns out worse than the soils report suggested, you’ll get a written change order with the new number before we do the work. Never a surprise invoice at the end. The allowance that isn’t on paper is a surprise waiting for a date. Call (877) 610-1318 to talk through your project and get a fixed bid.
Every additions and ADU job we complete in San Francisco carries the written 90-Day Done Right Promise. If something isn’t done right, Tom comes back and makes it right. One call. Beyond that, the materials we install carry manufacturer warranties from the brands we named, and we hand you those documents at closeout. Call (877) 610-1318 to schedule your free estimate, and ask Tom about the promise when you meet him; he’ll shake your hand and write it down.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Francisco and the surrounding Bay Area since 1998.